The present invention relates to a valve unit for use in controlling a fluid cylinder in a load sensing system. More particularly, the present invention relates to a selectively controlled valve unit having a priority flow valve that is manually adjustable and at least one lock check valve that is automatically responsive to fluid pressure within the system. A centrally located fluid passage within the valve unit supplies pilot or control fluid to the lock check valve. The location of the passage permits additional lock check valves to be easily installed.
In a typical valve unit, there is an inlet port connected to a fluid pump and a control spool to direct pressurized fluid from the pump to a fluid cylinder. The valve unit has raise, lower and neutral positions and is commonly used on, as for example; loaders, back hoes and agricultural implements.
A disadvantage of this conventional type of valve is the lack of a "float" position. Float is the ability of an implement to move gradually in either direction under its own weight, as for example, a large agricultural implement may float from a raised position to the transport position. Ordinarily, a separate mechanism is required to cause the float action which is inconvenient for the operator of the vehicle.
Another disadvantage of the typical valve unit is the inability to determine priority of fluid flow. Many valve units have priority valves to insure that one section of the system is satisfied before fluid is directed to another section. This priority is fixed and cannot be adjusted.